ASTM E3-11(2017)
(Guide)Standard Guide for Preparation of Metallographic Specimens
Standard Guide for Preparation of Metallographic Specimens
SIGNIFICANCE AND USE
4.1 Microstructures have a strong influence on the properties and successful application of metals and alloys. Determination and control of microstructure requires the use of metallographic examination.
4.2 Many specifications contain a requirement regarding microstructure; hence, a major use for metallographic examination is inspection to ensure that the requirement is met. Other major uses for metallographic examination are in failure analysis, and in research and development.
4.3 Proper choice of specimen location and orientation will minimize the number of specimens required and simplify their interpretation. It is easy to take too few specimens for study, but it is seldom that too many are studied.
SCOPE
1.1 The primary objective of metallographic examinations is to reveal the constituents and structure of metals and their alloys by means of a light optical or scanning electron microscope. In special cases, the objective of the examination may require the development of less detail than in other cases but, under nearly all conditions, the proper selection and preparation of the specimen is of major importance. Because of the diversity in available equipment and the wide variety of problems encountered, the following text presents for the guidance of the metallographer only those practices which experience has shown are generally satisfactory; it cannot and does not describe the variations in technique required to solve individual specimen preparation problems.
Note 1: For a more extensive description of various metallographic techniques, refer to Samuels, L. E., Metallographic Polishing by Mechanical Methods, American Society for Metals (ASM) Metals Park, OH, 3rd Ed., 1982; Petzow, G., Metallographic Etching, ASM, 1978; and VanderVoort, G., Metallography: Principles and Practice, McGraw Hill, NY, 2nd Ed., 1999.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E3 − 11(Reapproved 2017)
Standard Guide for
Preparation of Metallographic Specimens
This standard is issued under the fixed designation E3; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope A90/A90M Test Method for Weight [Mass] of Coating on
Iron and Steel Articles with Zinc or Zinc-Alloy Coatings
1.1 The primary objective of metallographic examinations
E7 Terminology Relating to Metallography
is to reveal the constituents and structure of metals and their
E45 Test Methods for Determining the Inclusion Content of
alloys by means of a light optical or scanning electron
Steel
microscope. In special cases, the objective of the examination
E768 Guide for Preparing and Evaluating Specimens for
may require the development of less detail than in other cases
Automatic Inclusion Assessment of Steel
but, under nearly all conditions, the proper selection and
E1077 Test Methods for Estimating the Depth of Decarbur-
preparation of the specimen is of major importance. Because of
ization of Steel Specimens
the diversity in available equipment and the wide variety of
E1122 Practice for Obtaining JK Inclusion Ratings Using
problems encountered, the following text presents for the
Automatic Image Analysis (Withdrawn 2006)
guidance of the metallographer only those practices which
E1245 Practice for Determining the Inclusion or Second-
experience has shown are generally satisfactory; it cannot and
Phase Constituent Content of Metals by Automatic Image
does not describe the variations in technique required to solve Analysis
individual specimen preparation problems. E1268 Practice for Assessing the Degree of Banding or
Orientation of Microstructures
NOTE 1—For a more extensive description of various metallographic
E1558 Guide for Electrolytic Polishing of Metallographic
techniques, refer to Samuels, L. E., Metallographic Polishing by Mechani-
Specimens
cal Methods, American Society for Metals (ASM) Metals Park, OH, 3rd
E1920 Guide for Metallographic Preparation of Thermal
Ed., 1982; Petzow, G., Metallographic Etching, ASM, 1978; and
Sprayed Coatings
VanderVoort, G., Metallography: Principles and Practice, McGraw Hill,
NY, 2nd Ed., 1999.
3. Terminology
1.2 This standard does not purport to address all of the
3.1 Definitions:
safety concerns, if any, associated with its use. It is the
3.1.1 For definitions used in this practice, refer to Termi-
responsibility of the user of this standard to establish appro-
nology E7.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 castable mount—a metallographic mount generally
1.3 This international standard was developed in accor-
made from a two component castable plastic. One component
dance with internationally recognized principles on standard-
is the resin and the other hardener. Both components can he
ization established in the Decision on Principles for the
liquid or one liquid and a powder. Castable mounts generally
Development of International Standards, Guides and Recom-
do not require heat and pressure to cure.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee. 3.2.2 compression mount—a metallographic mount made
using plastic that requires both heat and pressure for curing.
2. Referenced Documents
3.2.3 planar grinding—is the first grinding step in a prepa-
ration procedure used to bring all specimens into the same
2.1 ASTM Standards:
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This guide is under the jurisdiction of ASTM Committee E04 on Metallography contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
and is the direct responsibility of Subcommittee E04.01 on Specimen Preparation. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved June 1, 2017. Published June 2017. Originally the ASTM website.
approved in 1921. Last previous edition approved in 2011 as E3–11. DOI: The last approved version of this historical standard is referenced on
10.1520/E0003-11R17. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E3 − 11(2017)
plane of polish. It is unique to semi or fully automatic 5.2.2 In hot-worked or cold-worked metals, both transverse
preparation equipment that utilize specimen holders. and longitudinal sections should be studied. Special investiga-
tions may require specimens with surfaces prepared parallel to
3.2.4 rigid grinding disc—a non-fabric support surface,
the original surface of the product.
such as a composite of metal/ceramic or metal/polymer
5.2.3 In the case of wire and small rounds, a longitudinal
charged with an abrasive (usually 6 to 15μm diamond
section through the center of the specimen proves advanta-
particles), and used as the fine grinding operation in a metal-
geous when studied in conjunction with the transverse section.
lographic preparation procedure.
5.3 Transverse sections or cross sections taken perpendicu-
4. Significance and Use lar to the main axis of the material are often used for revealing
the following information:
4.1 Microstructures have a strong influence on the proper-
5.3.1 Variations in structure from center to surface,
ties and successful application of metals and alloys. Determi-
5.3.2 Distribution of nonmetallic impurities across the
nation and control of microstructure requires the use of
section,
metallographic examination.
5.3.3 Decarburization at the surface of a ferrous material
4.2 Many specifications contain a requirement regarding
(see Test Method E1077),
microstructure; hence, a major use for metallographic exami-
5.3.4 Depth of surface imperfections,
nation is inspection to ensure that the requirement is met. Other
5.3.5 Depth of corrosion,
major uses for metallographic examination are in failure
5.3.6 Thickness of protective coatings, and
analysis, and in research and development.
5.3.7 Structure of protective coating. See Guide E1920.
4.3 Proper choice of specimen location and orientation will 5.4 Longitudinal sections taken parallel to the main axis of
minimize the number of specimens required and simplify their
the material are often used for revealing the following infor-
interpretation. It is easy to take too few specimens for study, mation:
but it is seldom that too many are studied.
5.4.1 Inclusion content of steel (see Practices E45, E768,
E1122, and E1245),
5. Selection of Metallographic Specimens 5.4.2 Degree of plastic deformation, as shown by grain
distortion,
5.1 The selection of test specimens for metallographic
5.4.3 Presence or absence of banding in the structure (see
examination is extremely important because, if their interpre-
Practice E1268), and
tation is to be of value, the specimens must be representative of
5.4.4 The microstructure attained with any heat treatment.
the material that is being studied. The intent or purpose of the
5.5 The locations of surfaces examined should always be
metallographic examination will usually dictate the location of
the specimens to be studied. With respect to purpose of study, given in reporting results and in any illustrative micrographs. A
suitable method of indicating surface locations is shown in Fig.
metallographic examination may be divided into three classi-
fications: 1.
5.1.1 General Studies or Routine Work—Specimens should
6. Size of Metallographic Specimens
be chosen from locations most likely to reveal the maximum
variations within the material under study. For example,
6.1 For convenience, specimens to be polished for metallo-
specimens could be taken from a casting in the zones wherein
graphic examination are generally not more than about 12 to 25
maximum segregation might be expected to occur as well as
mm (0.5 to 1.0 in.) square, or approximately 12 to 25 mm in
specimens from sections where segregation could be at a
diameter if the material is cylindrical. The height of the
minimum. In the examination of strip or wire, test specimens
specimen should be no greater than necessary for convenient
could be taken from each end of the coils.
handling during polishing.
5.1.2 Study of Failures—Test specimens should be taken as
6.1.1 Larger specimens are generally more difficult to pre-
closely as possible to the fracture or to the initiation of the
pare.
failure. Before taking the metallographic specimens, study of
6.1.2 Specimens that are, fragile, oddly shaped or too small
the fracture surface should be complete, or, at the very least,
to be handled readily during polishing should be mounted to
the fracture surface should be documented. In many cases,
ensure a surface satisfactory for microscopical study. There
specimens should be taken from a sound area for a comparison
are, based on technique used, three fundamental methods of
of structures and properties.
mounting specimens (see Section 9).
5.1.3 Research Studies—The nature of the study will dictate
specimen location, orientation, etc. Sampling will usually be
7. Cutting of Metallographic Specimens
more extensive than in routine examinations.
7.1 In cutting the metallographic specimen from the main
5.2 Having established the location of the metallographic
body of the material, care must be exercised to minimize
samples to be studied, the type of section to be examined must
altering the structure of the metal. Three common types of
be decided.
sectioning are as follows:
5.2.1 For a casting, a section cut perpendicular to the 7.1.1 Sawing, whether by hand or machine with lubrication,
surface will show the variations in structure from the outside to is easy, fast, and relatively cool. It can be used on all materials
the interior of the casting. with hardnesses below approximately 350 HV. It does produce
E3 − 11(2017)
TABLE 1 Cutoff Blade Selection
Hardness Bond
Materials Abrasive Bond
HV Hardness
up to 300 non-ferrous (Al, Cu) SiC P or R hard
up to 400 non-ferrous (Ti) SiC P or R med.
hard
up to 400 soft ferrous Al O P or R hard
2 3
up to 500 medium soft ferrous Al O P or R med.
2 3
hard
up to 600 medium hard ferrous Al O P or R medium
2 3
up to 700 hard ferrous Al O P or R&R med. soft
2 3
up to 800 very hard ferrous Al O P or R&R soft
2 3
> 800 extremely hard ferrous CBN P or M hard
more brittle ceramics diamond P or M very hard
tougher ceramics diamond M ext. hard
P—phenolic
R—rubber
R&R—resin and rubber
M—metal
Symbol in
Suggested Designation cutoff blades on the specimen should be removed by some
Diagram
suitable organic solvent. Failure to clean thoroughly can
A Rolled surface
prevent cold mounting resins from adhering to the specimen
B Direction of rolling
surface. Ultrasonic cleaning may be effective in removing the
C Rolled edge
last traces of residues on a specimen surface.
D Planar section
E Longitudinal section perpendicular to rolled surface
8.2 Any coating metal that will interfere with the subse-
F Transverse section
G Radial longitudinal section quent etching of the base metal should be removed before
H Tangential longitudinal section
polishing, if possible. If etching is required, when studying the
underlying steel in a galvanized specimen, the zinc coating
FIG. 1 Method of Designating Location of Area Shown in Photo-
should be removed before mounting to prevent galvanic effects
micrograph.
during etching. The coating can be removed by dissolving in
cold nitric acid (HNO , sp gr 1.42), in dilute sulfuric acid
a rough surface containing extensive plastic flow that must be
(H SO ) or in dilute hydrochloric acid (HCl). The HNO
2 4 3
removed in subsequent preparation.
method requires care to prevent overheating, since large
7.1.2 An abrasive cut-off blade will produce a smooth
samples will generate considerable heat. By placing the clean-
surface often ready for fine grinding. This method of sectioning
ing container in cold water during the stripping of the zinc,
is normally faster than sawing. The choice of cut-off blade,
attack on the underlying steel will be minimized. More
lubricant, cooling conditions, and the grade and hardness of
information may be found in Test Method A90/A90M.
metal being cut will influence the quality of the cut. A poor
choice of cutting conditions can easily damage the specimen,
NOTE 2—Picral etchant produces little or no galvanic etching effects
when used on galvanized steel.
producing an alteration of the microstructure. Generally, soft
NOTE 3—The addition of an inhibitor during the stripping of Zn from
materials are cut with a hard bond blade and hard materials
galvanized coatings will minimize the attack of the steel substrate. NEP
with a soft bond blade. Aluminum oxide abrasive blades are
(polethylinepolyamine) or SbCl are two useful inhibitors.
preferred for ferrous metals and silicon carbide blades are
8.3 Oxidized or corroded surfaces may be cleaned as
preferred for nonferrous alloys. Abrasive cut-off blades are
described in Appendix X1.
essential for sectioning metals with hardness above about 350
HV. Extremely hard metallic materials and ceramics may be
9. Mounting of Specimens
more effectively cut using diamond-impregnated cutting
9.1 There are many instances where it will be advantageous
blades. Manufacturer’s instructions should be followed as to
to mount the specimen prior to grinding and polishing. Mount-
the choice of blade. Table 1 lists the suggested cutoff blades for
ing of the specimen is usually performed on small, fragile, or
materials with various Vickers (HV) hardness values.
oddly shaped specimens, fractures, or in instances where the
7.1.3 A shear is a type of cutting tool with which a material
specimen edges are to be examined.
in the form of wire, sheet, plate or rod is cut between two
opposing blades. 9.2 Specimens may be either mechanically mounted,
mounted in plastic, or a combination of the two.
7.2 Other methods of sectioning are permitted provided they
do not alter the microstructure at the plane of polishing. All 9.3 Mechanical Mounting:
cutting operations produce some depth of damage, which will
9.3.1 Strip and sheet specimens may be mounted by binding
have to be removed in subsequent preparation steps. or clamping
...
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